MFJ MFJ-213 - Checking Coax Cable; Testing RF Transformers

MFJ-213 HF/VHF/UHF Antenna Analyzer Instruction Manual
could be used. Shorter stubs will yield poorer accuracy and long ones may
needlessly waste useful cable.
7.6 Checking Coax Cable Impedance
To check a length of coax cable for impedance error, connect one end to the
analyzer and terminate the far end with a precision (non-inductive) 50-Ohm
resistive load. The cable will need to be at least 1-4 long at 30 MHz for this
test. Set the MFJ-213 up for analyzer mode and tune to 30 MHz. Rotate the
Tune between 15 and 60 MHz while watching the Jmpedance Magnitude
reading. If the cable is 50 Ohms and in good condition, there should be little
change in the impedance magnitude readings. If there are significant
fluctuations, the cable is either not 50 Ohms or is badly contaminated. If
readings cyclically swing between 25 Ohms and 100 Ohms, the cable is 75-
Ohm coax.
7.7 Testing RF Transformers
Broadband HF-matching transformers wound for the 12.5 to 200 Ohm range
may be tested using the MFJ-213. Connect the 50-Ohm (primary) side to the
analyzer connector using a short pigtail or binding post adapter, and attach
the appropriate resistive load across the secondary side (always use a non-
inductive resistor).
Next:
(1.) Set the MFJ-213 up in Analyzer mode (Section-3)
(2.) Set the Band to the desired frequency range (Section-4)
(3.) Rotate Tune across the frequency range and note SWR. Change bands,
as needed.
At the low and high ends of the transformer's frequency response range,
SWR and reactance will climb to unacceptable levels (< 1.2:1 is ideal). HF
tuned transmission-line transformers may be tested in similar fashion by
connecting one end directly to the analyzer and terminating the far end.
However, only precision RF terminations with known impedance
characteristics should be used above 50 MHz. Set up the analyzer for the
desired range and sweep the band of interest using the Tune control.
Transmission-line transformers are “frequency specific” and have much
more limited frequency response.
Version I 14 © 2012 MFI Enterprises, Inc